1. Field of the Invention
The present invention relates to transmission rate control methods, mobile stations, and radio network controllers, for controlling transmission rates of uplink user data.
2. Description of the Related Art
In a conventional mobile communication system, in an uplink from a mobile station UE to a radio base station Node B, a radio network controller RNC is configured to determine a transmission rate of a dedicated channel, in consideration of radio resources of the radio base station Node B, an interference volume in an uplink, transmission power of the mobile station UE, transmission processing performance of the mobile station UE, a transmission rate required for an upper application, and the like, and to notify the determined transmission rate of the dedicated channel by a message of a layer-3 (Radio Resource Control Layer) to both of the mobile station UE and the radio base station Node B.
Here, the radio network controller RNC is provided at an upper level of the radio base station Node B, and is an apparatus configured to control the radio base station Node B and the mobile station UE.
In general, data communications often cause burst traffic compared with voice communications or TV communications. Therefore, it is preferable that a transmission rate of a channel used for the data communications is changed fast.
However, as shown in FIG. 1, the radio network controller RNC integrally controls a plurality of radio base stations Node B in general. Therefore, in the conventional mobile communication system, there has been a problem that it is difficult to perform fast control for changing of the transmission rate of channel (for example, per approximately 1 through 100 ms), due to processing load, processing delay, or the like.
In addition, in the conventional mobile communication system, there has been also a problem that costs for implementing an apparatus and for operating a network are substantially increased even if the fast control for changing of the transmission rate of the channel can be performed.
Therefore, in the conventional mobile communication system, control for changing of the transmission rate of the channel is generally performed on the order from a few hundred ms to a few seconds.
Accordingly, in the conventional mobile communication system, when burst data transmission is performed as shown in FIG. 2(a), the data are transmitted by accepting low-speed, high-delay, and low-transmission efficiency as shown in FIG. 2(b), or, as shown in FIG. 2(c), by reserving radio resources for high-speed communications to accept that radio bandwidth resources in an unoccupied state and hardware resources in the radio base station Node B are wasted.
It should be noted that both of the above-described radio bandwidth resources and hardware resources are applied to the vertical radio resources in FIGS. 2(b) and 2(c).
Therefore, the 3rd Generation Partnership Project (3GPP) and the 3rd Generation Partnership Project 2 (3GPP2), which are international standardization organizations of the third generation mobile communication system, have discussed a method for controlling radio resources at high speed in a layer-i and a media access control (MAC) sub-layer (a layer-2) between the radio base station Node B and the mobile station UE, so as to utilize the radio resources effectively. Such discussions or discussed functions will be hereinafter referred to as “Enhanced Uplink (EUL)”.
Radio resource control methods that have been discussed in the “Enhanced Uplink” can be broadly categorized into three as follows. The radio resource control methods will be briefly described below.
First, a radio resource control method that is referred to as “Time & Rate Control” has been discussed.
In such a radio resource control method, a radio base station Node B determines a mobile station UE which can transmit user data and a transmission rate of user data of the mobile station UE per a predetermined timing, so as to signal information relating to a mobile station ID as well as the transmission rate of user data (or a maximum allowable transmission rate of user data).
The mobile station UE that is designated by the radio base station Node B transmits user data at the designated timing and the transmission rate (or within a range of the maximum allowable transmission rate).
Second, a radio resource control method that is referred to as “Rate Control per UE” has been discussed.
In such a radio resource control method, if there is user data that should be transmitted to the radio base station Node B, each mobile station UE can transmit the user data. However, the maximum allowable transmission rate of the user data, which is determined by the radio base station Node B and signaled to each mobile station UE for each transmission frame or each of a plurality of transmission frames, is used.
Here, when the maximum allowable transmission rate is signaled, the radio base station Node B signals the maximum allowable transmission rate itself, or one of three values (e.g., Up/Down/Hold command) as a relative value of the maximum allowable transmission rate at this timing.
Third, a radio resource control method that is referred to as “Rate Control per Cell” has been discussed.
In such a radio resource control method, a radio base station Node B signals a transmission rate of user data, which is common among mobile stations UE in communication, or information needed to calculate the transmission rate, and each mobile station UE determines a transmission rate of user data based on the received information.
Ideally, the “Time & Rate Control”, and the “Rate Control per UE” can be the best control methods for improving radio capacity in an uplink. However, a transmission rate of user data has to be granted after data volume stored in buffers of the mobile station UE, transmission power in the mobile station UE, or the like are grasped. Therefore, there has been a problem that control load is increased by the radio base station Node B.
In addition, in these radio resource control methods, there has been a problem that overhead becomes larger by exchanges of control signals.
On the other hand, in the “Rate Control per Cell”, there is an advantage in that control load by the radio base station Node B is small since the radio base station Node B signals information which is common in cells, and each mobile station UE autonomously seeks the transmission rate of user data based on the received information.
However, the radio base station Node B has to be configured in such a manner that the user data in the uplink from any mobile station UE can be received. Therefore, there has been a problem that an apparatus size of radio base station Node B becomes large to effectively utilize the radio capacity of the uplink.
Accordingly, there has been proposed, for example, a scheme (Autonomous ramping method) that the mobile station UE increases the transmission rate of user data from a pre-notified initial transmission rate in accordance with predetermined rules so that excessive allocation of radio capacity by the radio base station Node B can be prevented, thereby preventing increase of the apparatus size of radio base station Node B.
In such a scheme, a radio base station Node B determines a maximum allowable transmission rate (or parameters for the maximum allowable transmission rate. The same below.) based on hardware resources and radio bandwidth resources (for example, an interference volume in an uplink) in each cell, so as to control the transmission rate of user data in communicating mobile stations UE. Detailed descriptions of a control scheme based on hardware resources and a control scheme based on an interference volume in an uplink will be given below.
In the control scheme based on the hardware resources, a radio base station Node B is configured to signal a maximum allowable transmission rate to a mobile station UE connected to a cell under the control thereof.
The radio base station Node B lowers the maximum allowable transmission rate so as to avoid shortage of the hardware resources when the transmission rate of user data in the mobile station UE connected to the cell under the control thereof is increased and the hardware resources are insufficient.
On the other hand, the radio base station Node B again increases the maximum allowable transmission rate when the space of the hardware resources become larger at a time of completion of user data transmission in the mobile station UE connected to the cell under the control thereof, or the like.
In addition, in the control scheme based on the interference volume in the uplink, a radio base station Node B is configured to signal a maximum allowable transmission rate to a mobile station UE connected to a cell under the control thereof.
When the transmission rate of user data in the mobile station UE connected to the cell under the control of a radio base station Node B increases and a measured interference volume (for example, a measured noise rise) in the uplink exceeds an allowable value (for example, a maximum allowable noise rise), the radio base station Node B lowers the maximum allowable transmission rate so that the interference volume in the uplink can be within a range of the allowable value (see, FIG. 3).
On the other hand, when the interference volume (for example, the noise rise) in the uplink is within a range of the allowable value (for example, the maximum allowable noise rise), thereby having a space, at the time of completion of user data transmission in the mobile station UE connected to the cell under the control of the radio base station Node B, or the like, the radio base station Node B again increases the maximum allowable transmission rate (see, FIG. 3).
Also, it has been proposed that, as shown in FIG. 4, in a mobile communication system adopting the Autonomous ramping method, when a mobile station UE is performing a soft handover (SHO), a MAC-e function in a serving cell (e.g., cell #4) notifies the mobile station UE of a maximum allowable transmission rate of uplink user data, using an E-DCH Absolute rate Grant Channel (E-AGCH), and a MAC-e function in a non-serving cell (e.g., cell #3) instructs the mobile station UE to suppress a maximum allowable transmission rate by one of two types of commands, “Down command” or “Don't care command”, using an E-DCH Relative rate Grant Channel (E-RGCH).
In this manner, a maximum allowable transmission rate of uplink user data at a mobile station UE performing a soft handover can be reduced to reduce interference, increasing transmission efficiency (throughput) in an entire cell.
However, in the conventional mobile communication system using the Autonomous ramping method, it is necessary for a mobile station UE to receive an E-RGCH from one or more cells at each Transmission Time Interval (TTI) and to control speedily in response to the received E-RGCH. This causes the problem of increased complexity of the mobile station UE.